1. Field of the Invention
The present invention relates to the structure of a superconducting member, and more particularly, it relates to the structure of a superconducting member having excellent superconductivity, which is unrestrictedly formed on a substrate of an arbitrary base material.
2. Description of the Prior Art
In recent years, oxide superconducting materials having perovskite structure, such as those of La-Sr-Cu-O and Y-Ba-Cu-O, have been discovered in succession. Since such discovery, many studies have been made on these materials, which are higher in critical temperature than conventional superconducting materials such as alloys or intermetallic compounds of Nb-Ti, Nb-Ge and the like.
Such oxide superconducting materials are typically manufactured by powder sintering at present. For example, a superconducting wire rod is provided by filling powder of an oxide superconducting material in a metal pipe and performing wire drawing. In order to form a circuit, there has been proposed a method of kneading powder of an oxide superconducting material with an organic binder and printing the same. In either method, the powder is shaped into a linear or layer member, to be finally sintered. Thus, the powder member is inevitably shrunk in sintering, and hence it is difficult to obtain a final product of arbitrary configuration or size.
Every oxide superconductor heretofore discovered has high crystal anisotropy, and it is necessary to orient its crystal structure in order to obtain high critical current density. However, it is difficult to provide accurate orientation by sintering. Further, voids inevitably occur upon sintering, and hence it has been impossible to obtain an oxide superconductor having satisfactory critical current density by sintering.
On the other hand, an oxide superconductor having an arbitrary configuration can be easily obtained by preparing a base material with excellent workability depositing a superconducting film on the same, in a manner unlike the sintering process. In particular, such a superconducting film can be made by a vapor phase film process such as sputtering, which is excellent in crystal controllability, to easily obtain a dense film, as effective means for obtaining a superconductor having excellent properties.
In the case of forming a thin film on the base material, however, heating in an oxidizing atmosphere is required for performing heat treatment after film formation or for heating the substrate during film formation. Thus, the superconductivity tends to be reduced by oxidation of the base material or diffusion between a superconducting layer and the base material. In the method of forming a thin film on the base material, therefore, the base material is restricted to a high-priced material which is hard to work, such as SrTiO.sub.3 or MgO.
In particular, formation of an oxide superconducting film on a metal base material has not yet been studied since the base material is extremely oxidized and remarkable influence is exerted by diffusion between the superconducting layer and the base material. However, if a superconducting material is to be applied to an elongated member such as a tape, for example, it is preferable to employ a highly flexible metal substrate as a base material. Thus, the art requires a technique for forming an oxide superconducting layer on a substrate of an arbitrary base material.